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| Titel |
Contribution of long-range transport to the ozone levels recorded in the Northeast of Portugal |
| VerfasserIn |
C. Gama, T. Nunes, M. C. Marques, F. Ferreira |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250028221
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| Zusammenfassung |
| In the past four years (2004-2007), measurements carried out at Lamas de Olo, the only air
quality monitoring background station in the Northeast of Portugal, showed high ozone
concentrations (97,7±29,7 μg.m-3). This remote site, located in the middle of Alvão Natural
Park, in Portugal, 1086 m asl, plays a significant role on the total amount of exceedances
registered in the national air quality network.
The analysis of the data recorded at this monitoring station revealed an annual cycle of
ozone concentrations similar to the ones observed in other background sites of the Northern
Hemisphere (Monks, 2000; Vingarzan and Taylor, 2003). This common feature
comprises a distinct maximum during spring (peaking during the month of April).
Nevertheless it is during the summer that the hourly concentrations are higher, due to the
typical atmospheric and meteorological conditions that promote photochemical
pollution episodes. Photochemical pollution episodes can be related with production of
ozone in a local scale or in a global scale due to the transportation of polluted air
masses. For this reason analysing these events is crucial to fully understand the
behaviour of ozone in the Northeast of Portugal, in order to adopt the correct long-term
policies.
With the purpose of studying the influence of long-range transport on the ozone levels
recorded at Lamas de Olo, a cluster analysis was performed on 96-hour back trajectories air
masses. Different trajectory clusters represent air masses with different source regions of
atmospheric pollutants and the influence of these regions on the atmospheric composition at
the arrival point (receptor) of the trajectories can therefore be assessed (EMPA,
2008).
The back trajectories were simulated 4 times per day, using HYSPLIT model.
A “bottom-up” cluster methodology was used to group trajectories into clusters
according to their characteristics, for several time periods with similar ozone levels
and/or distributions. Ozone average levels were calculated for each cluster and the
differences between the groups were validated using the Kruskal-Wallis statistical
test.
The results have shown a significant influence of the transport path on ozone
concentrations, which is more noticeable when the probability of occurring photochemical
pollution phenomena is higher. Air masses from Europe (Spain, France, United
Kingdom, etc.) generally originate higher ozone levels than the ones arriving from the
Atlantic Ocean. This feature shows the role of photochemical production along
long-range transport phenomena, and the input of pollutants into air masses, along their
path.
A more detailed analysis at local/regional scale, supported mainly by an intensive field
campaign performed during spring/summer of 2006 in the vicinity of Alvão Natural Park
(FOTONET Project), at different altitudes, together with pollutant measurements from rural
air quality stations in the north of Portugal and one from Spain (Peñausende) was carried out
in order to evaluate the extension of photochemical pollution in the Northeast of Portugal.
Ozone concentrations measurements in the region showed a noticeable decrease with altitude,
mainly at night.
In resume back trajectories based analysis has demonstrated that other countries, mainly
Spain, contribute decisively to the ozone levels registered in the station used for this
study. Backed on this knowledge we point out towards the need of considering
common international policies when dealing with controlling ozone levels in the
environment.
References:
Monks, P. (2000): A review of the observations and origins of the spring ozone
maximum. Atmospheric Environment 34, 3545-3561.
Vingarzan, R., Taylor, B. (2003): Trend analysis of ground level ozone in the greater
Vancouver / Fraser Valley area of British Columbia. Atmospheric Environment 37,
2159-2171.
EMPA (2008): Air mass trajectory clustering. Retrieved 01 November 2008 from:
http://www.empa.ch/plugin/template/empa/*/63288/—/l=1 |
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